The dyeing of textiles, especially garments and fabrics of a synthetic material such as polyester, usually is carried out with a dyestuff dispersed in an aqueous bath. The textile material is placed in the bath for a long enough time period to allow sufficient dyestuff to be absorbed to provide the desired coloration.
Such a dyeing process poses several disadvantages and limitations. Since the temperature of the aqueous bath cannot exceed the boiling temperature of the water, the process cannot be conducted at elevated temperatures, unless high pressure is used. Even then temperatures of only 250.degree. F. to 270.degree. F. are reached. Consequently, relatively long dyeing cycles are needed.
Dyeing at elevated temperatures with a non-aqueous system overcomes many of these problems and provides several advantages. Elevated temperatures reduce the time needed to dye the textile material. Shorter dyeing cycles make the process more economical and efficient.
Various dye processes that use non-aqueous dye compositions have been proposed for the treatment of textile materials. One technique involves immersing the textile material in a bath with an organic dyestuff dissolved in a high-boiling, nonionic organic medium, such as a high-boiling aromatic ester or a cycloaliphatic diester. Such dyeing processes have several inherent disadvantages that prevent their effective and efficient use. The dye composition does not remain stable over a period of time when used in an ambient atmosphere. As reported in Clifford U.S. Pat. No. 4,550,579, significant degradation of the dye composition often occurs after only a few hours of use, especially at elevated temperatures.
In the entrainment dyeing process as described in copending, commonly-assigned U.S. application Ser. No. 067,799, filed June 30, 1987, the high-boiling dyeing medium behaves as a carrier fluid to allow the dyestuff to enter the fiber evenly. In that process, a significant amount, often as much as 50% to 120% by weight, of the dyeing medium is needed to smoothly apply the dyes due to the low solubility of most dyestuffs in the dyeing medium. The amount of high-boiling dyeing medium needed to perform the dye carrier fluid task is an amount much lower than the amounts mentioned above needed to apply the dyestuffs. It is desirable to reduce the amount of high-boiling media applied to the fabric due to a number of economic factors.
In addition, dyestuff solutions containing more than 5% by weight dyestuff are difficult to prepare. Mixing is also complicated by having to use powdered dyes. Cleanup of application equipment is slow because of the high viscosity of the medium dyestuff solution. The invention described in detail below provides solutions to all of these problems.